Answer: C) Participle phrase.
Explanation: a participle is a word formed from a verb and used as an adjective or a noun. A participle phrase is a group of words consisting of a participle and its modifiers (direct objects, indirect objects, or complements). In the given sentence, the phrase in brackets (sol at the farm store) is an example of a participle phrase (the participle is "sold") that acts as an adjective that is modifying the noun "pie."